Aviation is highly taxed (about half of your ticket). Subsidies (or more accurately tax discounts) are only on fuel which is something like 10% of your flight costs. Rest goes on staff and capex.

There already is form of transport that's much cheaper than train or flying which is called BUS. We can make them fully electric and even have different classes. They can share existing infrastructure that doesn't require thousands of specialised people to maintain or operate...